The experiments of single-bubble sonochemistry are measurements of rates of OH radical formation as well as \({\text{NO}}_{2}^{ - }\) and \({\text{NO}}_{3}^{ - }\) ions from a single stably pulsating bubble trapped near the pressure antinode of a standing ultrasonic field in the liquid. As the single-bubble system is very simple without any bubble–bubble interaction, it enables direct comparison between the experimental data and numerical simulations of chemical reactions inside a bubble. In other words, a theoretical model could be validated through the direct comparison with the experimental data of single-bubble sonochemistry. The experimental setup of single-bubble sonochemistry is the same as single-bubble sonoluminescence (SBSL) which is the light emission phenomenon from a single stably pulsating bubble. It has been shown that a SBSL bubble in water in which air is dissolved consists mainly of argon (which is 1% of air in molar fraction), called argon rectification. It has also been shown that the bubble temperature increases to about 10,000 K at the bubble collapse, and gas is weakly ionized inside the bubble (called plasma) due to the considerable lowering of ionization potential by high density inside the bubble at the collapse. It has been reported that the plasma is in non-equilibrium. Unsolved problems in SBSL as well as MBSL (multibubble sonoluminescence) are also discussed.